Joint and its manufacturing method

Abstract

To enhance joining rigidity between a first member and a second member.SOLUTION: A joining body 1 is constituted of a first material selected from a group including a metal material, a polymer material, a ceramic material and a complex material composed of these materials, and comprises a first member 10 in which a protrusion is formed at a front-side surface, and a second member 20 joined to the first member 10 at a front side of the first member 10, and constituted of a second material which includes at least the metal material. A joining part 21 of the second member 20 joined to the first member 10 is constituted of a fine grain structure which satisfies at least either of the fact that the a maximum crystal grain diameter is equal to or smaller than 100 μm, and the fact that an average crystal grain diameter is equal to or smaller than 30 μm.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a joined body in which a plurality of members are joined to each other and a method for manufacturing the same.

Background Art

[0002] Patent Document 1 discloses a joined product (joined body) having a first member and a second member having a larger coefficient of thermal expansion than the first member and joined to the first member, wherein the first member has a protrusion in which a part of the surface of the first member protrudes, and the second member is fitted to the protrusion on the joining surface between the first member and the second member.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the joined body disclosed in Patent Document 1, the second member is manufactured by casting (see paragraph 0018 of Patent Document 1, etc.). However, when the second member is manufactured by casting, the second member melts in the process and thus is composed of a melt-solidified structure. In the melt-solidified structure, crystal grains are non-uniform, and the joining strength between the first member and the second member may be insufficient.

[0005] The present invention has been made in view of such points, and an object thereof is to increase the joining strength between the first member and the second member.

Means for Solving the Problems

[0006] A first aspect of the present disclosure is a joint comprising a first member composed of a first material selected from the group including metallic materials, polymer materials, ceramic materials and composite materials thereof, and having protrusions on its front surface, and a second member joined to the first member on the front side of the first member and composed of a second material including at least a metallic material, wherein the joint portion of the second member that joins to the first member is composed of a fine-grained structure that satisfies at least one of the following conditions: the maximum grain size is 100 μm or less and the average grain size is 30 μm or less.

[0007] In this first embodiment, the joint portion of the second member joined to the first member is composed of a fine-grained structure that satisfies at least one of the following conditions: the maximum grain size is 100 μm or less and the average grain size is 30 μm or less. This makes it possible to increase the bonding strength between the first member and the second member.

[0008] A second aspect of the present disclosure, in the first aspect, the projection has a cross-sectional area augmentation portion such that the horizontal cross-sectional area, when cut in a horizontal direction parallel to the surface of the first member, increases as it moves away from the surface of the first member, and in a vertical cross-sectional view taken in a vertical direction perpendicular to the surface of the first member, the tangent line along the bottom of the circumferential surface intersects the surface of the first member at an acute angle. Herein, "tangent line" means the straight line itself, which is the shape of the circumferential surface, when the circumferential surface is straight in a vertical cross-sectional view.

[0009] In this second embodiment, the horizontal cross-sectional area of ​​the projection increases as it moves away from the surface of the first member, and the enlarged portion has a circumferential surface in which the tangent at its lowest point intersects the surface of the first member at an acute angle in a vertical cross-sectional view. As a result, the anchoring effect of the projection increases the joint strength between the first member and the second member. Furthermore, by adjusting the angle at which the tangent of the circumferential surface of the enlarged portion intersects the surface of the first member, the anchoring effect per projection can be increased and / or the number of projections per unit area can be increased (i.e., the number density of projections can be increased). In other words, by adjusting the angle, the joint strength between the first member and the second member can be further increased.

[0010] A third aspect of the present disclosure, in the first or second aspect, the projection has a cross-sectional area augmentation portion such that the horizontal cross-sectional area, when cut in a horizontal direction parallel to the surface of the first member, increases as it moves away from the surface of the first member, the cross-sectional area augmentation portion is polygonal in a horizontal cross-sectional view when cut in a horizontal direction parallel to the surface of the first member, and adjacent projections are arranged with their sides facing each other.

[0011] In this third embodiment, the projections increase in horizontal cross-sectional area as they move away from the surface of the first member, and have polygonal cross-sectional enlargements in a horizontal cross-sectional view. When such projections are arranged so that the sides of the enlarged cross-sectional areas face each other when adjacent projections are connected, the stress on the second member is more easily distributed between these adjacent projections when an external force is applied in a direction that pulls the first and second members apart. As a result, the second member becomes less likely to fracture between adjacent projections, and the joint strength between the first and second members can be further increased.

[0012] A fourth aspect of this disclosure is a manufacturing method for manufacturing a joint according to the first to third aspects, comprising a protrusion forming step of forming the protrusion of the first member by an additive manufacturing method.

[0013] In this fourth embodiment, the joint according to the first to third embodiments can be manufactured. Furthermore, since the protrusions are formed by an additive manufacturing method, it is easier to form the protrusions into a shape that further increases the joint strength.

[0014] A fifth aspect of the present disclosure further includes, in the fourth aspect, a joining step of joining the second member to the first member, wherein the joining step involves flowing the portion of the second member facing the first member in a solid state to form the joint portion composed of a non-molten solidified structure.

[0015] In the sixth embodiment, in the fifth embodiment, the joining step is to form the joint portion, which is composed of a non-molten solidified structure, by friction stirring.

[0016] In these fifth and sixth aspects, a joint portion composed of a non-molten solidified structure can be formed, so that the joint strength between the first member and the second member can be increased.

[0017] A seventh aspect includes a processing step of removing an attachment at the tip of the protrusion after the protrusion forming step and before the joining step in the fifth or sixth aspect.

[0018] In this seventh aspect, since the processing step is performed before the joining step, an attachment that weakens the joining between the protrusion and the surface of the second member can be removed. As a result, the joint strength between the first member and the second member is further increased.

Effect of the Invention

[0019] As described above, according to the present invention, the joint strength between the first member and the second member is increased.

Brief Description of the Drawings

[0020] [Figure 1] It is a plan view showing a first member of a joined body according to the first embodiment from the front side. [Figure 2] It is a vertical cross-sectional view of the joined body. [Figure 3] It is a schematic view showing a joining step in a method for manufacturing a joined body. [Figure 4] It is a view corresponding to FIG. 1 according to the first modification of the first embodiment. [Figure 5] It is a view corresponding to FIG. 2 according to the second modification of the first embodiment. [Figure 6] It is a view corresponding to FIG. 2 according to the third modification of the first embodiment. [Figure 7] It is a graph showing the results of tensile tests of joined bodies according to Examples 1 and 2 and Comparative Examples 1 and 2. [Figure 8] [[ID=I44]]It is a graph showing the results of tensile tests of joined bodies according to Examples 3 and 4. [Figure 9] It is a SEM image of a cross-section of a joined body according to Example 1. [Figure 10]This is an SEM image of the cross-section of the joint according to Comparative Example 2. [Figure 11] This is an SEM image of the cross-section of the joint according to Example 3. [Figure 12] This is an SEM image of the cross-section of the joint according to Example 4. [Figure 13] Figure 9 shows an image obtained by EBSD analysis of a SEM image. [Figure 14] Figure 10 shows an image obtained by EBSD analysis of a SEM image. [Figure 15] Figure 13 is a graph showing the grain size distribution in the image shown. [Figure 16] Figure 14 is a graph showing the grain size distribution in the image shown. [Figure 17] This image shows the maximum stress distribution per unit area in the joint model according to Example 10. [Figure 18] This image shows the maximum stress distribution per unit area in the joint model according to Example 11. [Modes for carrying out the invention]

[0021] Embodiments of the present invention will be described in detail below with reference to the drawings. The following description of preferred embodiments is essentially illustrative and is not intended to limit the present invention, its applications, or its uses.

[0022] (First Embodiment) —Structure of the joint— As shown in Figures 1 and 2, the jointed body 1 according to the first embodiment comprises a first member 10 made of a first material which is a metal material, and a second member 20 made of a second material which is a metal material, which is joined to the first member 10 on the front side of the first member 10.

[0023] Specifically, the first member 10 has a plurality of protrusions 11, 11, ... on its front surface. Each protrusion 11 is circular in plan view, as shown in Figure 1, and its horizontal cross-section, when cut along a direction parallel to the surface 12 of the first member, is also circular. Furthermore, each protrusion 11 is formed such that its diameter increases in proportion to its distance from the surface 12 of the first member, as shown in Figure 2. That is, each protrusion 11 is composed of a cross-sectional area increasing portion 11a, where the horizontal cross-sectional area increases as it moves away from the surface 12 of the first member. Note that the materials used to make up the protrusions 11 and the parts of the first member 10 other than the protrusions 11 may be different.

[0024] As shown in Figure 2, in a vertical cross-sectional view of the circumferential surface of the increased cross-section portion 11a, the tangent line intersects the first member surface 12 at an acute angle with respect to the first member surface 12. A tangent line is a straight line along the circumferential surface in a vertical cross-sectional view, and in Figure 2, the straight line representing the circumferential surface is the tangent line.

[0025] The dimensions of each projection 11 are not particularly limited, and according to the manufacturing method of the present invention, they can be formed in a wide range of sizes, for example, on the order of several hundred μm to mm. That is, the height H of each projection 11, the diameter L1 of the part with the smallest horizontal cross-sectional area in the cross-sectional enlargement portion 11a (hereinafter, the area of ​​this part will be referred to as "minimum horizontal cross-sectional area A1"), and the diameter L2 of the part with the largest horizontal cross-sectional area (hereinafter, the area of ​​this part will be referred to as "maximum horizontal cross-sectional area A2") are, for example, on the order of several hundred μm to mm.

[0026] Of the multiple protrusions 11,11,..., the distance D between the centers of the closest adjacent protrusions 11,11 is preferably not made too large from the viewpoint of providing many protrusions per unit area (i.e., increasing the number density of protrusions 11) and thereby increasing the overall joint strength.

[0027] In a vertical cross-sectional view (Figure 2), the angle θ between the tangent to the circumferential surface of each protrusion and the surface 12 of the first member is preferably small enough to increase the diameter L2 at the tip of each protrusion, from the viewpoint of maximizing the anchoring effect of each individual protrusion 11. On the other hand, from the viewpoint of maximizing the number of protrusions per unit area (maximizing the number density of protrusions) and increasing the overall joint strength, it is preferable to increase the angle θ so that the tips of the area-enlarged portions 11a do not get too close to each other between adjacent protrusions 11, 11.

[0028] Considering all of the above points comprehensively, it is preferable to set the angle θ accordingly.

[0029] The second member 20 has a joint portion 21 that joins with the first member 10. The joint portion 21 is composed of a fine-grained structure. Specifically, as shown in Figure 2, the joint portion 21 refers to the region of the second member 20 from the surface 12 of the first member to the front side by approximately twice the protrusion height H. A "fine-grained structure" is a non-molten solidified structure obtained, for example, by flowing in a solid state as in the present invention. Such a non-molten solidified structure has higher uniformity of crystal grain size and smaller crystal grains compared to a molten solidified structure obtained by casting or the like. In the present invention, a fine-grained structure means satisfying at least one of the following conditions: the maximum crystal grain size is 100 μm or less and the average crystal grain size is 30 μm or less.

[0030] Furthermore, most of the space S on the back side of the cross-sectional enlargement portion 11a is filled with the second material that constitutes the joint portion 21. Here, the space S on the back side of the cross-sectional enlargement portion 11a refers to the space on the back side of the cross-sectional enlargement portion 11a (the side of the first member surface 12) and inside the region enclosed by the outer peripheral surface of the outermost part of the cross-sectional enlargement portion 11a (the dot-hatched region represented by symbol A2 in Figure 1), as shown by the dot hatching in Figure 2. From the viewpoint of increasing the joint strength between the first member 10 and the second member 20, it is preferable that 50% or more of the volume of such space S is filled with the second material, more preferably 70% or more of the volume is filled with the second material, and even more preferably 90% or more of the volume is filled with the second material.

[0031] Furthermore, the ratio A1 / A2, obtained by dividing the minimum horizontal cross-sectional area A1 of the increased cross-sectional area portion 11a by the maximum horizontal cross-sectional area A2, is preferable to be smaller from the viewpoint of making it more difficult for one projection 11 to come loose from the joint portion 21 and thereby increasing the joint strength.

[0032] —Method for manufacturing a jointed body— The manufacturing method for the jointed body 1 includes a preparation step of preparing the first member 10 and the second member 20 by molding them from a first material and a second material, respectively; a protrusion formation step of forming the protrusions 11 of the first member 10 by an additive manufacturing method; and a joining step of joining the second member 20 to the first member 10. The additive manufacturing method used in the protrusion formation step is not particularly limited, but examples include powder bed fusion bonding, directed energy deposition, binder injection bonding, and fused deposition.

[0033] In the joining process, as shown in Figure 3, the portion 22 of the second member 20 facing the first member 10 is made to flow in a solid state by friction stirring, thereby forming a joint 21 composed of a non-molten solidified structure. In other words, in the joining process, the portion 22 of the second member 20 facing the first member 10 is stirred while remaining in a solid state (without melting).

[0034] As shown in Figure 3, friction stirring involves inserting a substantially cylindrical joining tool T, which has screw threads formed on its circumferential surface, into the second member 20 by frictional heat and rotational force while rotating it in the circumferential direction, simultaneously stirring the solid-state second material while causing it to plastically flow. In this way, the stirred second material fills the entire area around the projection 11, including the front and back sides of the projection 11, and a second member 20 is obtained that is joined to the first member 10.

[0035] At this time, as shown in Figure 3, it is preferable to stir the second material while pressing the screw threads of the joining tool T against the tip surface of the projection 11 in order to remove the tip surface of the projection 11 with the screw threads of the joining tool T. The depth of the tip surface of the projection 11 to be removed by the joining tool T is, for example, 0.4 mm or less. By removing the tip surface of the projection 11 in this way, it is possible to remove the contaminating layer consisting of deposits such as oil and oxides that adhere to the tip surface of the projection 11 and weaken the bond with the surface of the second member 20, as well as the protective film which will be explained in the modified example of the second embodiment described later.

[0036] Furthermore, during the joining process, it is not necessary to grind the tip surface of the projection 11 with the threads of the joining tool T, and there may be a gap between the threads and the tip surface of the projection 11.

[0037] The direction in which the joining tool T is inserted is not limited to the direction shown in Figure 3. For example, the joining tool T may be inserted into the second member from a direction perpendicular to the surface 12 of the first member. The goal is to allow the second material to plastically flow and fill the entire area around the projection 11.

[0038] —Effects and Actions— In this embodiment, the joint portion 21 of the second member 20 that is joined to the first member 10 is composed of a fine-grained structure (non-molten solidified structure), and the joint strength between the first member 10 and the second member 20 is greater than when the joint portion 21 is composed of a molten solidified structure.

[0039] Furthermore, in this embodiment, the projection 11 has a cross-sectional area augmentation portion 11a whose horizontal cross-sectional area increases as it moves away from the surface 12 of the first member. The cross-sectional area augmentation portion 11a has a circumferential surface whose tangent intersects the surface 12 of the first member at an acute angle in a vertical cross-sectional view (Figure 2), thereby increasing the joint strength between the first member 10 and the second member 20 due to the anchoring effect of the projection 11. In addition, by adjusting the angle θ at which the circumferential surface of the projection 11 intersects the surface 12 of the first member, the anchoring effect of each projection 11 can be increased, and / or the number of projections that can be densely packed per unit area can be increased. That is, by adjusting the angle θ, the joint strength between the first member 10 and the second member 12 can be further increased.

[0040] Furthermore, in this embodiment, more than 50% of the volume of the space S on the back side of the cross-sectional enlargement portion 11a is filled with the second material constituting the joint portion 21, so that the joint portion 21 functions reliably as a retainer and the anchoring effect of the projection 11 is increased. As a result, the joint strength between the first member 10 and the second member 20 is further increased.

[0041] Incidentally, as shown in Comparative Examples 1 and 2 described later, when the second member 20 is manufactured by casting and joined to the first member 10, it was found that the back side of the cross-sectional enlargement portion 11a is not sufficiently filled with the second material. This is particularly noticeable when the size of the protrusion 11 is small. In this embodiment, however, the second member 20 is not cast but joined to the first member 10 by friction stir processing while in a solid state, so that the back side of the cross-sectional enlargement portion 11a is reliably filled with the second material, and the joint portion 21 functions reliably as a retainer. In other words, the joint portion exhibits a high anchoring effect.

[0042] Furthermore, the manufacturing method of this embodiment can produce a jointed body 1 that exhibits the effects described above.

[0043] Furthermore, in the manufacturing method of this embodiment, the tip surface of the projection 11 is scraped with the joining tool T during the joining process, so that the contaminating layer consisting of oil, oxides, and other deposits adhering to the tip surface of the projection 11 that weaken the bond with the surface of the second member 20, as well as the protective film described in the modified example of the second embodiment described later, can be removed. As a result, the bonding strength between the first member 10 and the second member 20 is further increased.

[0044] Furthermore, the manufacturing method of this embodiment allows the use of materials that are difficult to weld by melting (for example, copper, aluminum, etc.) in terms of melting point, thermal conductivity, coefficient of thermal expansion, and gas solubility.

[0045] Furthermore, the joint and its manufacturing method according to the present invention are useful in a very wide range of fields where it is necessary to join two members. For example, they can be used for joining vehicle components such as reinforcements and brackets to improve the strength of the vehicle body, and for joining three-dimensional structural members such as hemmed joints and box corners. They can also be used when the butt joint surface is large (thick), such as in butt joints of rods or thick plates, like those in automobile suspension arms.

[0046] Furthermore, the method for manufacturing a joint according to the present invention can join a first member 10 and a second member 20 made of dissimilar materials. If the first member 10 and the second member 20 are made of materials with different properties such as mechanical properties, electrical properties, and thermal properties, it is possible to create a unique member that combines the advantages of each material. For example, it can be applied to body panels and frames of products aimed at weight reduction. It can also handle the joining of curves, such as the disc and rim portions of a wheel, and even with cylindrical members such as motor cases, a hybrid motor case with both strength and heat dissipation can be created by overlapping and joining the outer pipe and inner pipe. In this way, it is possible to impart various properties to members of various shapes.

[0047] (First embodiment, first modified example) Figures 4 to 6 show the shapes of the protrusions 11 in the joint 1 according to the first to third modified examples of the first embodiment, respectively. The configuration of the joint 1 according to each modified example is the same as that of the first embodiment, except for the shape of the protrusions 11.

[0048] Specifically, in the first modified example, as shown in Figure 4, each projection 11 is square in plan view, and like each projection 11 in the first embodiment, the entire projection is an enlarged cross-section portion 11a. In this modified example, the enlarged cross-section portion 11a is polygonal in a horizontal cross-sectional view when cut in a horizontal direction parallel to the surface 12 of the first member, and adjacent projections 11, 11 are arranged with their sides facing each other. "Arranged with their sides facing each other" means that, as shown in Figure 4, one side of the outline of one projection 11 in plan view (or horizontal cross-sectional view) is approximately parallel to one side of the outline of an adjacent projection 11 in plan view (or horizontal cross-sectional view), and "approximately parallel" is not limited to being perfectly parallel, but includes one side being offset from the other side by a small angle of 10° or less.

[0049] As shown in this modified example, when adjacent protrusions 11, 11 are arranged with their edges in the cross-sectional enlargement portion 11a facing each other, as shown in Examples 5 to 10 described later, when an external force is applied in a direction that pulls the first member 10 and the second member 20 apart, the stress on the second member 20 is more easily distributed between the adjacent protrusions 11, 11. As a result, the second member 20 becomes less likely to break between the adjacent protrusions 11, 11, and the joint strength between the first member 10 and the second member 20 increases.

[0050] (Second modified example of the first embodiment) In the second modified example, as shown in Figure 5, each projection 11 is approximately spherical, and the area from the surface 12 of the first member to approximately the vertical center of each projection 11 is the cross-sectional enlargement portion 11a. Even with the projection 11 as shown in Figure 5, in a vertical cross-sectional view, the tangent line along the lowest part of the circumferential surface of the cross-sectional enlargement portion 11a intersects the surface 12 of the first member at an acute angle. As a result, the anchoring effect of the projection 11 increases the joint strength between the first member 10 and the second member 20.

[0051] (Third modified example of the first embodiment) In the third modified example, as shown in Figure 6, each projection 11 has a support portion 11b formed on the surface 12 of the first member and a substantially spherical tip portion 11c formed on the front side of the support portion 11b. The horizontal cross-section of the support portion 11b is, for example, circular, elliptical, or polygonal, and its horizontal cross-sectional area decreases as it moves away from the surface 12 of the first member. For this reason, the area around the connection between the support portion 11b and the tip portion 11c is constricted in a vertical cross-sectional view (Figure 6), and the area from this constricted connection to the approximate vertical center of the tip portion 11c constitutes the cross-sectional enlargement portion 11a.

[0052] Even with the projection 11 shown in Figure 6, in a vertical cross-sectional view, the tangent line along the lowest part of the circumferential surface of the increased cross-sectional area 11a intersects the surface 12 of the first member at an acute angle. As a result, the anchoring effect of the projection 11 increases the joint strength between the first member 10 and the second member 20.

[0053] (Second Embodiment) In the second embodiment, the method for manufacturing the joined body 1 differs from the first embodiment in the following respects, but is otherwise the same as the first embodiment. In this embodiment, a processing step is included, performed after the protrusion formation step and before the joining step, to remove deposits from the tip surface (tip portion) of the protrusion 11. Here, "deposits" refers to impurities (contamination layer) such as oil and oxides that weaken the bond between the protrusion 11 and the surface of the second member 20, or a protective film which will be explained in the modified example described later. In the processing step, for example, the tip surface of the protrusion is cleaned.

[0054] In this embodiment, the processing step is performed before the joining step, so that any deposits that weaken the bond between the projection 11 and the surface of the second member 20 can be removed. As a result, the bonding strength between the first member 10 and the second member 20 is further increased.

[0055] Furthermore, since the tip surface of the projection 11 is treated during the processing step, the contaminated layer can be removed from the tip surface of the projection 11 without having to grind it with the screw threads of the joining tool T during the joining process, thus simplifying the joining process.

[0056] (Modified version of the second embodiment) In a modified version of the second embodiment, in the manufacturing method according to the second embodiment, after the processing step, the tip surface of the projection 11 is protected by, for example, plating or electrodeposition to form a protective film. This makes it less likely for a contaminated layer to form on the tip surface of the projection 11 even if the first member 10 is stored in the atmosphere for a long period of time. When joining the second member 20 to the first member 10 after long-term storage, the processing step can be performed on the tip surface of the projection 11 to remove the protective film.

[0057] (Other embodiments) The shapes and arrangements of the multiple protrusions 11, 11, ... are not limited to those of the embodiments described above. For example, the shape of the protrusion 11 may be an ellipse, rectangle, parallelogram, rhombus, triangle, or other polygon in plan view, in addition to a circle or square. Also, the cross-sectional enlargement portion 11a of the protrusion 11 may enlarge in a step-like manner, rather than gradually increasing as in the embodiments described above. Furthermore, the sizes and shapes of the multiple protrusions 11, 11, ... may differ from each other. For example, the protrusions according to the first embodiment and its various modifications may be mixed together.

[0058] Furthermore, in each of the above embodiments, friction stir processing is used as a method for forming the joint 21 by flowing the second material in a solid state, but other methods such as friction welding and press working may also be used.

[0059] Furthermore, the first and second materials are not limited to those of the embodiments described above. For example, the first material may be a composite material of a polymer material, a ceramic material, or any combination of all of these materials. The second material may be a composite material of a metal material and a non-metallic material, such as plastic or ceramics. If the second material is such a composite material, it is sufficient that the metal material contained in the second material constitutes a non-molten solidified structure (fine-grained structure).

[0060] Furthermore, in each of the above embodiments, the joint 1 is composed of a first member 10 and a second member 20, but it is sufficient for multiple members to be joined to each other. For example, in addition to the first member 10 and the second member 20, a third member may be joined to the first member 10 or the second member 20. [Examples]

[0061] —Evaluation Test— Below, we describe Examples 1 to 4, in which a joint 1 according to the first embodiment and its first modified example was manufactured and the joint strength between the first member 10 and the second member 20 in each joint 1 was evaluated, as well as Comparative Examples 1 and 2 for comparison therewith.

[0062] [Example 1] <Preparation process> A rectangular parallelepiped first member, measuring 150 mm in length, 35 mm in width, and 15 mm in thickness, was prepared from steel (first material). A rectangular parallelepiped second member, also measuring 150 mm in length, 35 mm in width, and 15 mm in thickness, was prepared from aluminum alloy (A5052) (second material).

[0063] <Protrusion formation process> Next, a protrusion was formed on the side surface of the first member (a surface with a width of 35 mm and a thickness of 15 mm) using an additive manufacturing method, with maraging steel (first material) as the material. The shape of the protrusion was the same as in the above embodiment, as shown in Figures 1 and 2. The parameters were D=5.7 mm, L1=1.7 mm, L2=3.7 mm, and θ=45°. The minimum horizontal cross-sectional area A1 of the increased cross-sectional area was 2.3 mm². 2 The maximum horizontal cross-sectional area A2 is 11 mm². 2 The ratio of the two, A1 / A2, was 0.21.

[0064] <Joining process> Next, as shown in Figure 3, the joining tool was inserted into the second member while rotating at a rotational speed of 1800 rpm, and the solid-phase second material was stirred to join the second member to the first member. At this time, the screw threads on the circumferential surface of the joining tool were slightly spaced from the tip surface of the protrusions, and the tip surface of the protrusions was not machined. Furthermore, while stirring the second material, the joining tool was moved in the longitudinal direction of the second member at a speed of 25 mm / min, thereby joining the second member to each protrusion of the first member along its entire length. The joined body was manufactured in this manner.

[0065] Table 1 shows the conditions for the protrusion formation process and joining process in Examples 1-4 and Comparative Examples 1 and 2.

[0066] [Table 1]

[0067] [Comparative Example 1] In Comparative Example 1, the first member was prepared in the same manner as in Example 1, but the second member was prepared by casting. Specifically, the second material was melted and poured onto the surface of the first member on which the protrusions were formed, and then cooled to form the second member and join it to the first member. Furthermore, an AC4C aluminum alloy with good castability was used as the second material. All other conditions were the same as in Example 1.

[0068] [Example 2] In Example 2, the joint was manufactured in the same manner as in Example 1, except that each parameter was different, as shown in Table 1.

[0069] [Comparative Example 2] In Comparative Example 2, the joint was manufactured in the same manner as in Comparative Example 1, except that the parameters were different.

[0070] [Example 3] In Example 3, the shape of the protrusion was made square in plan view, as shown in Figure 4, and each parameter was set to the values ​​shown in Table 1. In addition, during the joining process, the threads on the circumferential surface of the joining tool T were pressed against the protrusion, and the tip surface of the protrusion was machined to a depth of approximately 0.2 mm. Except for the above points, the joined body was manufactured under the same conditions as in Example 1.

[0071] [Example 4] In Example 4, during the joining process, the screw threads on the circumferential surface of the joining tool T were spaced slightly away from the tip surface of the projection, and the tip surface of the projection was not machined. Except for this point, the joined body was manufactured in the same manner as in Example 3.

[0072] [Tensile test] First, the joints manufactured in each example and comparative example were formed into dumbbell-shaped test specimens, with one end half composed of a first member and the other end half of a second member. That is, the boundary between the first and second members was located in the longitudinal center of each test specimen. Next, using a tensile testing machine (Shimadzu Corporation, product name: UH-100kNXR), both ends of each test specimen were pulled in opposite directions.

[0073] Figure 7 shows the tensile test results for Examples 1 and 2 and Comparative Examples 1 and 2. In all examples and comparative examples, as the test force applied by the tensile testing machine increased, the elongation and stress of the test specimen increased, and when the stress value exceeded the material's limit, the material fractured. Examples 1 and 2, in which the second member was formed by friction stir processing and the two members were joined together, showed higher maximum stresses compared to Comparative Examples 1 and 2, in which the second member was cast and the two members were joined together. In other words, Examples 1 and 2 have greater joint strength between the two members compared to Comparative Examples 1 and 2.

[0074] Furthermore, as shown in Figure 7, the maximum stress in Example 2 is greater than the maximum stress in Example 1. This is thought to be because Example 2 has more protrusions than Example 1, resulting in a greater overall anchoring effect of the protrusions, and consequently, a greater joint strength between the first and second members.

[0075] Figure 8 shows the results of the tensile tests for Examples 3 and 4. In all examples, the first and second members were joined by friction stir machining. However, in Example 3, where the tip surfaces of the protrusions were machined with a joining tool during friction stir machining, the maximum stress was approximately 2.5 times greater than in Example 4, where the tip surfaces of the protrusions were not machined. This indicates that the joint strength was approximately 2.5 times greater.

[0076] [SEM image] Figures 9 and 10 show SEM images of cross-sections of the joints according to Example 1 and Comparative Example 2, respectively. From Figure 9, it can be seen that in the joint according to Example 1, the space on the back side of the protrusion (the surface side of the first member) is almost 100% filled with the aluminum alloy of the second member. From this, it can be concluded that in Example 1, since the aluminum alloy is filled on the back side of the enlarged cross-section, the anchoring effect of the protrusion is increased, and as a result, the joint strength between the first member and the second member is increased.

[0077] In contrast, Figure 10 clearly shows that in the joint according to Comparative Example 2, on average, less than 50% of the volume of the space behind the protrusion is filled with aluminum alloy, indicating a large proportion of defective areas where aluminum alloy is not filled. From this, it can be concluded that in Comparative Example 2, despite the shape of the protrusion having an enlarged cross-sectional area at the tip, the protrusion is not sufficiently secured, and the anchoring effect is not sufficiently obtained, resulting in a reduced joint strength between the first and second members.

[0078] Figures 11 and 12 show SEM images of cross-sections of the joints according to Examples 3 and 4, respectively. In both Examples 3 and 4, it can be seen that in each joint, the space on the back side of the protrusion (the surface side of the first member) is filled almost 100% of its volume with the aluminum alloy of the second member.

[0079] Furthermore, in Figure 12, a thin gap can be seen on the tip surface of the protrusion (see the thin black layer indicated by the arrow). This is thought to be an unjointed area in the joint according to Example 4, because the tip surface of the protrusion was not scraped with the joining tool during the joining process, a contaminating layer composed of deposits such as oil and oxides was not removed. In contrast, as can be seen from Figure 11, no such thin gap is observed in the joint according to Example 3. Therefore, it is thought that in Example 4, the presence of the aforementioned contaminating layer resulted in a lower joint strength between the first and second members compared to Example 3.

[0080] [EBSD analysis] Figures 13 and 14 show the results of EBSD (Electron-Backscatter Diffraction) analysis performed on the areas enclosed by dashed lines in the SEM images shown in Figures 9 and 10, respectively. As a result of the EBSD analysis, in Figures 13 and 14, the outlines of the crystal grains of the second material on the back side of each protrusion are drawn with black lines. In Figures 13 and 14, the other black areas indicate defect areas where neither maraging steel nor either material is filled, which forms the protrusion. In Figure 14, the outlines of the protrusions are shown with white dashed lines. In the joint according to Comparative Example 2 shown in Figure 14, it can be seen that the crystal grains of the second material on the back side of the protrusions are larger and their size is generally non-uniform compared to the joint according to Example 1 shown in Figure 13.

[0081] To examine these crystal grains in detail, Figures 15 and 16 show graphs where the distribution ratio of the crystal grains (second material) shown in Figure 13 (Example 1) and Figure 14 (Comparative Example 2) is plotted on the vertical axis, and the grain size is plotted on the horizontal axis, respectively. It can be seen that the grain size distribution in Figure 15 (Example 1) is highly uniform, while the grain size distribution in Figure 16 (Comparative Example 2) is non-uniform. Furthermore, in Example 1, the maximum grain size was smaller than 85 μm, and the average grain size was 24 μm. In contrast, in Comparative Example 1, the maximum grain size was larger than 160 μm, and the average grain size was 70 μm. Thus, the grain size in Example 1 is generally small, which is thought to be because the joining method was friction stir welding, which involves flow in a solid state, rather than casting as in Comparative Example 1.

[0082] -simulation- Next, the joint strength of a joint formed by joining a first member, which has a circular protrusion in a plan view as shown in Figure 1, and a second member was evaluated by simulation using the general-purpose software "Simufact Forming 2021" (manufactured by HEXAGON). In this simulation, the joint force between the first member and the second member was evaluated in a joint model that included a first member having one protrusion and another adjacent protrusion of the same shape, and a second member joined to this first member.

[0083] Specifically, in the following, simulations were performed on joint models according to Examples 5 to 16, in which at least one of the parameters that determine the shape of the protrusions, H, L1, L2, and θ, the distance between the centers of the protrusions D, and the nearest neighbor distance D0, differs from each other. In each simulation, when the first and second members of each joint model were pulled from each other, the maximum value of the load that changes as the distance (mm) between the two members increases (hereinafter referred to as "maximum load") (kN), or the value obtained by dividing this maximum load by the area of ​​the interface between the two members (hereinafter referred to as "maximum stress") (MPa), was calculated, and the joint force between the two members was evaluated.

[0084] In the following simulation, the peripheral edges of the projection tips in each joint model are chamfered. The nearest neighbor distance D0 varies depending on the distance D between the projection centers and the tip surface diameter L2, but it also varies depending on the degree of chamfering.

[0085] [Examples 5-7] In Example 5, the parameters were set as follows: D=4.24mm, D0=0.72mm, H=1.00mm, L1=1.10mm, L2=3.52mm, and θ=35°. In Examples 6 and 7, as shown in Table 2, θ=45° and 60°, respectively. That is, in Examples 5, 6, and 7, the angle θ of the projection circumferential surface increases in this order, and the diameter L2 of the projection tip surface decreases accordingly, but the distance D between the centers of the projections and the projection height H remain unchanged.

[0086] [Table 2]

[0087] The maximum load was calculated for each joint model in Examples 5 to 7. By comparing these maximum loads across Examples 5 to 7, it is possible to evaluate the joint force obtained per protrusion, independent of the number density of protrusions.

[0088] As shown in Table 2, the calculated maximum load is highest in Example 5, where L2 is the largest and θ is the smallest. This result is thought to reflect that in Example 5, the anchoring effect of one protrusion is larger due to the large L2 and smallest θ, resulting in greater joint strength.

[0089] [Examples 8-12] In Example 8, the parameters were set as follows: D=2.90mm, H=1.00mm, L1=1.10mm, L2=2.82mm, and θ=45°. In Examples 9-12, as shown in Table 3, the parameters were set as follows: D=2.97mm, 3.11mm, 3.39mm, and 4.24mm, respectively. In other words, in Examples 8, 9, 10, 11, and 12, the distance between the centers of the projections D and the nearest neighbor distance D0 increase in this order, but the shape of the projections (H, L1, L2, θ) remains unchanged.

[0090] [Table 3]

[0091] The maximum stress was calculated for each joint model in Examples 8 to 12. By comparing these maximum stresses in Examples 8 to 12, it is possible to evaluate the jointing force of a joint in which countless protrusions are arranged at equal intervals D (D0) on the first member, that is, the jointing force considering the number density of the protrusions.

[0092] As shown in Table 3, the maximum stress is highest in Example 11, where D = 3.39 mm (D0 = 0.58 mm). To investigate the reason for this, the distribution of maximum stress on the protrusion and the second member was calculated for Examples 8 to 12. It was found that the larger D (D0), the smaller the localization of the maximum stress on the second member.

[0093] Figures 17 and 18 show distribution images of maximum stress in the joint models according to Examples 10 and 11, respectively. These images show the distribution of the maximum stress on two adjacent protrusions and the maximum stress on the second member between these protrusions, displayed in grayscale, in a horizontal cross-section (horizontal cross-section at the protrusion tip surface) 1.00 mm away from the surface of the first member. As shown in Figures 17 and 18, the maximum stress on the second member is highest at the point where the distance between the protrusions is smallest. In Figure 17 (Example 10), the point where the distance between the protrusions of the second member is smallest has a greater locally applied maximum stress compared to Figure 18 (Example 11), indicating a higher probability of the second member fracturing at this point. In other words, the larger the nearest neighbor distance D0, the less localized the maximum stress on the second member becomes, and therefore the less likely the second member is to fracture.

[0094] On the other hand, the smaller the distance D between the centers of the protrusions, the higher the number density of the protrusions. In other words, from the viewpoint of increasing the number density of protrusions and thereby improving joint strength, it is better to have the distance D between the centers of the protrusions as small as possible. As shown in Table 3, the reason why the maximum stress is highest in Example 11 is thought to be determined by two factors: the delocalization of the maximum stress applied to the second member and the number density of the protrusions.

[0095] Furthermore, as shown in Figure 17, when the first member is provided with a circular projection in plan view as shown in Figure 1, the maximum stress on the second member becomes localized. From this, it can be considered that if the shape of the projection is a square in plan view as shown in Figure 4, or if it is a different polygon, arranging adjacent projections so that the sides of the polygons face each other can suppress the localization of the maximum stress on the second member, thereby avoiding the second member becoming prone to fracture.

[0096] [Examples 13-16] In Example 13, the shape parameters were set to D=3.39mm (D0=0.58mm), H=1.00mm, L1=1.10mm, L2=2.82mm, and θ=45°. In Examples 14-16, D=2.55mm, 2.12mm, and 1.75mm, respectively, and θ=60°, 70°, and 80°. That is, in Examples 13, 14, 15, and 16, the angle θ of the projection surface increases in this order, and the projection tip surface diameter L2 and the distance D between projection centers decrease, but the projection height H remains unchanged.

[0097] [Table 4]

[0098] The maximum stress was calculated for each joint model in Examples 13 to 16. According to Table 4, the maximum stress is highest in Example 15. This result can be explained as follows. First, when the projection height H is constant, a larger L2 (a smaller θ) results in a greater anchoring effect of a single projection. Also, as discussed above, a smaller distance D between projection centers allows for a higher number density of projections, resulting in a higher maximum stress. In other words, the result that the maximum stress is highest in Example 15 is thought to be determined by two factors: the anchoring effect of a single projection and the number density of projections. [Industrial applicability]

[0099] The joint and method for manufacturing the same according to the present invention are useful in a very wide range of fields where it is necessary to join two members. [Explanation of symbols]

[0100] 1 zygote 10 First Member 11 Protrusions 11a Cross-sectional area 12 First Member Surface 20 Second Member 21 Joint 22 The part of the second member facing the first member

Claims

1. A first member comprising a first material selected from the group including metal materials, polymer materials, ceramic materials, and composite materials thereof, and having protrusions on its front surface, A second member is joined to the first member on the front side of the first member and is made of a second material which includes at least a metal material. Equipped with, A method for manufacturing a joint, wherein the joint portion of the second member that joins with the first member is composed of a fine-grained structure that satisfies at least one of the following conditions: the maximum grain size is 100 μm or less and the average grain size is 30 μm or less, The process includes a protrusion formation step in which the protrusion of the first member is formed by an additive manufacturing method, A joining step of joining the second member to the first member Includes, A manufacturing method comprising the joining process, wherein the portion of the second member facing the first member is made to flow in a solid state by friction stir processing or friction pressure welding, thereby forming the joint portion composed of a non-molten solidified structure.

2. In the manufacturing method described in claim 1, A manufacturing method comprising a processing step, which is performed after the projection forming step and before the joining step, for removing deposits from the tip of the projection.

3. In the manufacturing method according to claim 1 or 2, A manufacturing method comprising the following steps: inserting a joining tool having screw threads into the second member, and performing the friction stir machining.

4. In the manufacturing method according to any one of claims 1 to 3, A manufacturing method comprising the joining step of applying a rotational force to the second member in a direction parallel or perpendicular to the surface of the first member, thereby causing the portion of the second member facing the first member to flow in a solid state.

5. In the manufacturing method according to any one of Claims 1 to 4, The projection has a portion with an increased cross-sectional area, such that as it moves away from the surface of the first member, the horizontal cross-sectional area when cut in a horizontal direction parallel to the surface of the first member increases. A manufacturing method wherein 50% or more of the volume of the space on the back side of the enlarged cross-section is filled with the second material that constitutes the joint.

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